Lacquer reducing lubricating oil composition and method of use of same

ABSTRACT

This invention relates to lubricating oil compositions that have surprisingly been shown to reduce the formation of lacquer deposits in engines. More specifically, this invention relates to a lubricating oil for natural gas engines that reduces siloxane-related cylinder liner lacquer deposits.

FIELD OF INVENTION

[0001] This invention relates to lubricating oil compositions that have surprisingly been shown to reduce the formation of lacquer deposits in engines. More specifically, this invention relates to a lubricating oil for natural gas engines that reduces cylinder liner lacquer deposits.

BACKGROUND OF INVENTION

[0002] Over the last few years, natural gas fueled engines have become increasingly popular as they generate energy efficiently and economically while limiting environmental pollution. These features have resulted in numerous applications of natural gas fueled engines. For example, combined generation of heat and power, also known as co-generation, has achieved overall system efficiencies of over 90 percent. Another well know application is the use of these engines in natural gas compression and transmission. The engine is connected to a compressor (either piston or rotaly screw design) which takes natural gas from an underground reserve and sends it through supply pipelines; these engines typically either operate on the raw untreated gas, treated gas, or pipeline-quality gas.

[0003] Another effective use of natural gas fueled engines is the generation of electricity from landfill, bio, sewer or digester gas and other methane generation methods previously considered “waste” gasses. Instead of releasing the gas to the atmosphere or flaring off, the gas is used to generate electricity in natural gas fueled engines. However, these gasses tend to be contaminated and costly methods of gas treatment (e.g. sweetening, filtration) are sometimes employed. These contaminants can also necessitate more frequent engine maintenance.

[0004] Although the contamination could be measured by directly determining the concentration of each contaminant within the gas, this would be a costly and lengthy process and would not provide useful information to the engine operator in all cases. Natural gas engine manufacturers recognized quite early that the heating value of natural gas not only varied by its natural constituents (percentage of methane, ethane, butane, etc.), but also its entrained contaminants (water, etc.). As such, they referred to the Higher Heating Value (HHV) and Lower Heating Value (LHV) of a natural gas. The HHV is the amount of heat generated by burning one unit of the gas to complete combustion. Unfortunately this is not totally useful to an engine operator, as it does not account for the energy expended in changing the state of the entrained contaminants and of the water produced from the combustion. The LHV is the HHV less the amount of heat used to evaporate the water formed by combustion and other entrained contaminants. More information and the calculation of LHV may be determined from ANSI/ASME B.133.7M-1985, which is herein incorporated by reference.

[0005] The change in LHV has long been used to predict the combustion efficiency of natural gas engines. An increase in LHV can lead to over temperature operation which may cause hot spots in the combustion chamber. If the gas engine is operated under this condition for a period of time, the useful life of its internal parts may be reduced. On the other hand if the LHV decreases, the control system calls for an increase in fuel flow in order to maintain the power output of the engine, which may cause incomplete combustion and a drop in efficiency. In the case of very low LHV, the required fuel flow for maximum power output may exceed the specification of the fuel supply system and hence the desired power output may not be achieved.

[0006] However, the wide and often non-continuous variability of LHV made it difficult for natural gas engine operators to predict the proper air/fuel ratio for most efficient combustion. The more useful Wobbe Index was developed allowing engine operators to maintain a steady air/fuel ratio for a given Wobbe Index. The Wobbe Index of a specific fuel stream directed to an engine is determined by the equation: ${WI} = {{LHV}\frac{\sqrt{\rho_{air}}}{\sqrt{\rho_{fuel}}}}$

[0007] where the LHV is determined as above, and the ρ_(air) and ρ_(fuel) are the density of the incoming air and fuel stream to the engine at standard conditions (101.3 kPa and 273.15°K). The standard metric units for the Wobbe Index (and the LHV) are MJoules/m³. Further determination of the Wobbe Index may be found in SAE Technical Paper 861578, “Interchangeability of Gaseous Fuels—The Importance of the Wobbe-Index”, 1986, which is herein incorporated by reference.

[0008] One concern in all engines, including natural gas fired engines is the formation of deposits and lacquer and a resultant potential increase in lube oil consumption. Lacquer is a deposit resulting from the oxidation and polymerization of fuels and lubricants when exposed to high temperatures. Noting that the term is often used interchangeably with varnish, the CRC Deposit Rating Manual 20 defines lacquer as “a thin, hard, lustrous, oil-insoluble deposit, composed primarily of organic residue, and most readily definable by color intensity. It is not easily removed by wiping with a clean, dry, soft, lint-free wiping material and is resistant to saturated solvents. Its color may vary, but it usually appears in gray, brown, or amber hues.”

[0009] The problems associated with lacquer formation vary as to the location of the lacquer. Lacquer is known to form both on pistons and on the cylinder liners. While piston lacquer has often been discussed in the art, it differs from cylinder liner lacquer. Piston lacquer appears to be a high temperature phenomena, forming on the lands, grooves, skirt and undercrown of the piston. One current theory is that the formation of lacquer on these hot locations is a function of the oxidative stability of the lube oil. Therefore, a lubricating oil employing a Group II base oil should produce less piston lacquer than one employing a Group I base oil.

[0010] The mechanism of cylinder liner lacquer formation differs from piston lacquer as the cylinder liners generally operate at lower temperature. Cylinder liner lacquer is generally formed over the range of the top piston ring travel, that is, on the cylinder walls below the liner dead space (also known as the “squish area”) and above the top compression ring at the bottom of piston travel. In distillate or heavy fueled marine diesel engines, a partially clogged injector may lead to improper spray patterns. It is well known that irregular fuel impingement on the cylinder liner walls accelerates liner lacquer formation.

[0011] “Lean-burn” gas engines, as opposed to those that operate at stoichiometric air/fuel ratios (“rich burn” engines) have shown increasing problems due to the organic silicon compounds (“siloxanes”) often contained in the natural gas they employ. Engines that run on biogas, landfill gas or sewer gas are particularly susceptible to this problem. Siloxanes have been shown to increase the deposits on the cylinder heads, in areas of close tolerance or small-diameter passageways and increase lacquer on the cylinder liners. After as little as 1000 operating hours, lacquer buildup or other damage may occur that necessitates the exchange of the cylinder liners.

[0012] In extreme cases, the lacquer will fill in the cylinder liner cross hatching grooves which are vital for providing a uniform, protective oil film. Lube oil consumption, a major operating cost for these engines, can increase dramatically. This may result in bore polish, scuffing and scoring of the cylinder liners. Contrary to the theory of lacquer formation on hot surfaces, it is theorized that the solubility characteristics of the base oil mixture are more important than its oxidative stability for cylinder liner lacquer formation.

[0013] Many prior researchers had noticed some anti-varnish properties as a secondary effect in various complex formulations. For example, Gatto (U.S. Pat. No. 6,147,035) noted anti-varnish effects in a molybdenum based formulation. Bardasz (U.S. Pat. No. 5,595,964) teaches anti-varnishing characteristics when employing borated epoxides and hydrocarbylamine phosphate salts. Sougawa (U.S. Pat. No. 6,147,035) noted improvements in lacquer tests when employing a salicylate based formulation. However, none of the prior art has suggested the efficacy of the formulation of the present invention, nor on its unexpected reduction of cylinder liner lacquer or of lacquer deposits when used with non-Group I base stocks.

[0014] As is well known in the art, there are many advantages of using Group II, III and IV base stocks for lubricating oils. However, cylinder liner lacquer would be expected to become a more pronounced problem in modern lubricating oils that employ more highly saturated Group II, Group III and Group IV base oils, as their high paraffinicity also causes them to provide less solubility for modern additives and combustion produced contaminants. As such, lubricants developed from Group II base stocks have traditionally required more aggressive and carefully balanced additive systems to limit lacquering. Recent studies have shown that cylinder liner lacquer formation is further exacerbated in engines operated on landfill gas; current theory is that the increase is due to the entrained organic silicon compounds in the landfill gas.

[0015] A lubricating oil composition that performs adequately in one engine at given operating conditions does not necessarily perform adequately when used in a different engine or under different conditions. This is especially true for natural gas fueled engines. While theoretically, lubricants could be designed for each possible combination of engine and service condition, such a strategy would be impractical because many different types of engines exist and the engines are used under widely varying conditions. Accordingly, lubricants that perform well in different types of engines and across a broad spectrum of conditions (e.g., fuel type, operating load and temperature) are desired. Design of lubricating oil compositions is further complicated in that the concentrated mixture of chemicals added to lubricating oil base stocks to impart desirable properties should perform well over a broad range of different quality base stocks. Meeting these requirements has been very difficult because the formulations are complicated, tests to ascertain whether a lubricant performs well are very expensive and time consuming, and collecting field test data is frequently difficult since variables cannot be fully controlled. While piston deposit formation has often been controlled by mixtures of detergents and dispersants, controlling lacquer formation, especially cylinder liner lacquer formation, has been a more difficult objective to solve.

SUMMARY OF INVENTION

[0016] The present invention provides a method of reducing lacquer formation in an internal combustion engine by using a lubricant comprising:

[0017] (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks;

[0018] (b) a diarylamine, preferably an alkylated diphenyl amine;

[0019] (c) an alkaline earth metal phenate;

[0020] (d) an alkaline earth metal sulfonate;

[0021] (e) a borated aminated hydrocarbyl succinic derivative.

[0022] The present invention more specifically provides a method of reducing cylinder liner lacquer in internal combustion engines employing the above formulation.

DETAILED DESCRIPTION OF INVENTION

[0023] It has been found that use of an aromatic antioxidant, an alkaline earth metal phenate sulfide detergent, a borated aminated hydrocarbyl succinic derivative, and an alkaline earth metal sulfonate detergent as essential components in a specific combination and in particular proportions makes it possible to obtain a lubricating oil composition, especially a natural gas powered internal engine lubricating oil composition, that reduces the formation of lacquer. More specifically, it has been found that this composition is far superior to others when at least about 20 wt % of the final lubricant is made from a Group II base stock.

[0024] In one aspect, the present invention relates to a lubricating oil composition characterized in that the composition comprises a mixture of the following components:

[0025] (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks;

[0026] (b) about 0.05 to about 2 wt % of an alkylated diphenyl amines;

[0027] (c) about 0.05 to about 5 wt % of at least one overbased alkaline earth metal phenate;

[0028] (d) about 0.50 to about 5 wt % of a neutral or overbased alkaline earth metal sulfonate; and

[0029] (e) about 1.0 to about 10 wt % of a borated aminated hydrocarbyl succinic derivative.

[0030] In one aspect, the present invention relates to a lubricating oil composition characterized in that the composition comprises a mixture of the following components:

[0031] (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks;

[0032] (b) about 0.1 to about 1.0 wt % of an alkylated diphenyl amines;

[0033] (c) about 0.75 to about 4.0 wt % of at least one overbased alkaline earth metal phenate;

[0034] (d) about 0.5 to about 3.0 wt % of a neutral or overbased alkaline earth metal sulfonate; and

[0035] (e) about 1.5 to about 6.0 wt % of a borated aminated polyalkenyl succinic derivative.

[0036] In another embodiment, the present invention comprises a lubricating oil composition that reduces lacquering in natural gas powered engines characterized in that the composition comprises a lubricating base oil and a mixture of the following components:

[0037] (a) at least about 40 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks;

[0038] (b) about 0.20 to about 0.75 wt % of an alkylated diphenyl amines;

[0039] (c) about 0.9 to about 2.7 wt % of at least one overbased calcium phenate sulfide;

[0040] (d) about 0.50 to about 1.0 wt % of neutral calcium sulfonate; and

[0041] (e) about 1.75 to about 3.0 wt % of a borated aminated polybutenyl succinic anhydride derivative;

[0042] One aspect of the present invention is an additive system for use in a lubricating oil comprising at least about 20% of a Group II base stock, said additive comprising portions (b) through (e) of the above formulations, alone or when in a diluent. In another aspect, the present invention provides a method of reducing cylinder liner lacquer using the formulations outlined above.

[0043] The base oil for the lubricant of the present invention may be a mineral or synthetic oil or blends thereof, so long as about at least 20% is a non-Group I base stock as defined by API. A wide range of base stocks and base oils are known in the art. Base stocks and base oils that may be used as co-base stocks or co-base oils in combination with the base stocks and base oils of the present invention are natural oils, mineral oils, and synthetic oils. These lubricant base stocks and base oils may be used individually or in any combination of mixtures with the instant invention. Natural, mineral, and synthetic oils (or mixtures thereof) may be used unrefined, refined, or rerefined (the latter is also known as reclaimed or reprocessed oil). Unrefined oils are those obtained directly from a natural, mineral, or synthetic source and used without added purification. These include shale oil obtained directly from retorting operations, petroleum oil obtained directly from primary distillation, and ester oil obtained directly from an esterification process. Refined oils are similar to the oils discussed for unrefined oils except refined oils are subjected to one or more purification steps to improve at least one lubricating oil property. One skilled in the art is familiar with many purification processes. These processes include for example solvent extraction, distillation, secondary distillation, acid extraction, base extraction, filtration, percolation, dewaxing, hydroisomerization, hydrocracking, hydrofinishing, and others. Rerefined oils are obtained by processes analogous to refined oils but using an oil that has been previously used.

[0044] Groups I, II, III, IV and V are broad categories of base oil stocks developed and defined by the American Petroleum Institute (API Publication 1509; www.API.org) to create guidelines for lubricant base stocks and base oils. Group I base stocks generally have a viscosity index of between about 80 to 120 and contains greater than about 0.03wt % sulfur and/or less than about 90% saturates. Group II base stocks generally have a viscosity index of between about 80 to 120, and contain less than or equal to about 0.03 wt % sulfur and greater than or equal to about 90% saturates. Group III stocks generally have a viscosity index greater than about 120 and contain less than about 0.03 wt % sulfur and greater than or equal to about 90% saturates. Group IV includes polyalphaolefins (PAO). Group V base stock includes base stocks not included in Groups I-IV. The table below summarizes properties of each of these five Groups. TABLE 1 API Classification of Base stocks and base oils Saturates (wt %) Sulfur (wt %) Viscosity Index Group I <90 &/or ≧0.03% & ≧80 & ≦120 Group II ≧90 & <0.03% & ≧80 & ≦120 Group III ≧90 & <0.03% & >120 Group IV Polyalphaolefins (PAO) Group V All other base stocks and base oils not included in Groups I, II, III, or IV

[0045] Base stocks and base oils may be derived from many sources. Natural oils include animal oils, vegetable oils (castor oil and lard oil, for example), and mineral oils. In regard to animal and vegetable oils, those possessing favorable thermal oxidative stability can be used. Of the natural oils, mineral oils are preferred. Mineral oils vary widely as to their crude source, for example, as to whether they are paraffinic, naphthenic, or mixed paraffinic-naphthenic. Oils derived from coal or shale are also useful in the present invention. Natural oils vary also as to the method used for their production and purification, for example, their distillation range and whether they are straight run or cracked, hydrorefined, or solvent extracted.

[0046] Synthetic oils include hydrocarbon oil. Hydrocarbon oils include oils such as polymerized and interpolymerized olefins (polybutylenes, polypropylenes, propylene isobutylene copolymers, ethylene-olefin copolymers, and ethylene-alphaolefin copolymers, polymers or copolymer of hydrocarbyl-substituted olefins where hydrocarbyl optionally contains O, N, or S, for example). Polyalphaolefin (PAO) oil base stocks are a commonly used synthetic hydrocarbon oil. By way of example, PAOs derived from C8, C10, C12, C14 olefins or mixtures thereof may be utilized. See U.S. Pat. Nos. 4,956,122; 4,827,064; and 4,827,073, which are incorporated herein by reference in their entirety.

[0047] The PAO fluids may be conveniently made by the polymerization of an alphaolefin in the presence of a polymerization catalyst such as the Friedel-Crafts catalysts including, for example, aluminum trichloride, boron trifluoride or complexes of boron trifluoride with water, alcohols such as ethanol, propanol or butanol, carboxylic acids or esters such as ethyl acetate or ethyl propionate. For example the methods disclosed by U.S. Pat. No. 4,149,178 or U.S. Pat. No. 3,382,291 may be conveniently used herein. Other descriptions of PAO synthesis are found in the following U.S. Pat. Nos. 3,742,082; 3,769,363; 3,876,720; 4,239,930; 4,367,352; 4,413,156; 4,434,408; 4,910,355; 4,956,122; and 5,068,487. The dimers of the C14 to C18 olefins are described in U.S. 4,218,330. All of the aforementioned patents are incorporated by reference herein in their entirety.

[0048] Other synthetic base stocks and base oils include hydrocarbon oils that are derived from the oligomerization or polymerization of low-molecular weight compounds whose reactive group is not olefinic, into higher molecular weight compounds, which may be optionally reacted further or chemically modified in additional processes (e.g. isodewaxing, alkylation, esterification, hydroisomerization, dewaxing, etc.) to give a base oil of lubricating viscosity.

[0049] Other useful lubricant oil base stocks include wax isomerate base stocks and base oils, comprising hydroisomerized waxy stocks (e.g. waxy stocks such as gas oils, slack waxes, fuels hydrocracker bottoms, etc.), hydroisomerized Fischer-Tropsch waxes, Gas-to-Liquids (GTL) base stocks and base oils, and other wax isomerate hydroisomerized base stocks and base oils, or mixtures thereof. Fischer-Tropsch waxes, the high boiling point residues of Fischer-Tropsch synthesis, are highly paraffinic hydrocarbons with very low sulfur content. The hydroprocessing used for the production of such base stocks may use an amorphous hydrocracking/hydroisomerization catalyst, such as one of the specialized lube hydrocracking (LHDC) catalysts or a crystalline hydrocracking/hydroisomerization catalyst, preferably a zeolitic catalyst. For example, one useful catalyst is ZSM-48 as described in U.S. Pat. No. 5,075,269. Processes for making hydrocracked/hydroisomerized distillates and hydrocracked/hydroisomerized waxes are described, for example, in U.S. Pat. Nos. 2,817,693; 4,975,177; 4,921,594 and 4,897,178 as well as in British Patent Nos. 1,429,494; 1,350,257; 1,440,230 and 1,390,359. Particularly favorable processes are described in European Patent Application Nos. 464546 and 464547. Processes using Fischer-Tropsch wax feeds are described in U.S. Pat. Nos. 4,594,172 and 4,943,672. Gas-to-Liquids (GTL) base stocks and base oils, Fischer-Tropsch wax derived base stocks and base oils, and other wax isomerate hydroisomerized (wax isomerate) base stocks and base oils be advantageously used in the instant invention, and may have useful kinematic viscosities at 100° C. of about 3 cSt to about 50 cSt. These Gas-to-Liquids (GTL) base stocks and base oils, Fischer-Tropsch wax derived base stocks and base oils, and other wax isomerate hydroisomerized base stocks and base oils may have useful pour points of about −20° C. or lower, and under some conditions may have advantageous pour points of about −25° C. or lower, with useful pour points of about −30° C. to about −40° C. or lower. Useful compositions of Gas-to-Liquids (GTL) base stocks and base oils, Fischer-Tropsch wax derived base stocks and base oils, and wax isomerate hydroisomerized base stocks and base oils are recited in U.S. Pat. Nos. 6,080,301; 6,090,989, and 6,165,949 for example, and are incorporated herein in their entirety by reference.

[0050] The diarylamines useful in this invention are well known antioxidants and there is no particular restriction on the type of diarylamine that can be used. Preferably, the diarylamine is a secondary diarylamine and has the general formula:

[0051] wherein R1 and R2 each independently represents a substituted or unsubstituted aryl group having from 6 to 30 carbon atoms. Illustrative of substituents for the aryl group include aliphatic hydrocarbon groups such as alkyl having from about 1 to 30 carbon atoms, hydroxy groups, halogen radicals, carboxyl groups or nitro groups. The aryl is preferably substituted or unsubstituted phenyl or naphthyl, particularly wherein one or both of the aryl groups are substituted with at least one alkyl having from 4 to 30 carbon atoms, preferably from 4 to 18 carbon atoms. It is further preferred that both aryl groups be substituted, e.g. alkyl substituted phenyl.

[0052] The diarylamines used in this invention can be of a structure other than that shown in the above formula that shows but one nitrogen atom in the molecule. Thus, the diarylamine can be of a different structure provided that at least one nitrogen has 2 aryl groups attached thereto, e.g., as in the case of various diamines having a secondary nitrogen atom as well as two aryls on one of the nitrogens.

[0053] The diarylamines used in this invention should be soluble in the formulated crankcase oil package. Examples of some diarylamines that may be used in this invention include: diphenylamine; various alkylated diphenylamines, 3-hydroxydiphenylamine; N-phenyl-1,2-phenylenediamine; N-phenyl-1,4-phenylenediamine; dibutyldiphenylamine; dioctyldiphenylamine; dinonyldiphenylamine; phenyl-alpha-naphthylamine; phenyl-beta-naphthylamine; diheptyldiphenylamine; and p-oriented styrenated diphenylamine, mixed butyloctyldiphenylamine, and mixed octylstylyldiphenylamine.

[0054] Examples of commercial diarylamines include, for example, Irganox® L06 and Irganox® L57 from Ciba Specialty Chemicals; Naugalube® AMS, Naugalube® 438, Naugalube® 438R, Naugalube® 438L, Naugalube® 500, Naugalube® 640, Naugalube® 680, and Naugard® PANA from Uniroyal Chemical Company; Vanlube® DND, Vanlube® NA, Vanlube® PNA, Vanlube® SL, Vanlube® SLHP, Vanlube® SS, Vanlube® 81, Vanlube® 848, and Vanlube® 849 20 from R.T. Vanderbilt Company, Inc.

[0055] The concentration of the diarylamine in the lubricating composition can vary depending upon the customer's requirements and applications. In a preferred embodiment of the invention, a practical diarylamine use range in the lubricating composition is from about 500 parts per million to 20,000 parts per million (i.e. 0.05 to 2.0 wt %) based on the total weight of the lubricating oil composition, preferably the concentration is from 1,000 to 10,000 parts per million (ppm) and more preferably from about 2,000 to 7,500 ppm by weight.

[0056] As used herein and in the claims the term “phenate” means the broad class of metal phenates including salts of alkylphenols, alkylphenol sulfides, and the alkylphenol-aldehyde condensation products. Detergents formed from the polar phenate substrate may be overbased. Normal phenate has the structural formula:

[0057] whereas phenate sulfide has the formula:

[0058] wherein R₃ and R₄ are individually alkyl groups preferably of eight or more carbon atoms, M is a metallic element (e.g. Ca, Ba, Mg), and x may range from 1 to 3 depending on the particular metal involved. The calcium phenates is preferred for use in the present invention.

[0059] Overbased alkaline-earth metal phenates are often referred to by the amount of total basicity contained in the product. It is common to label a detergent by its TBN (total base number), i.e. a 300 TBN synthetic sulfonate. Base number is defined in terms of the equivalent amount of potassium hydroxide contained in the material. A 300 TBN calcium sulfonate contains base equivalent to 300 milligrams of potassium hydroxide per gram or, more simply, 300 mg KOH/g.

[0060] The alkaline-earth metal phenates useful in the present invention should have TBN's of from about 100 to 400, with 100 to 300 being more preferred. TBN's may be determined using ASTM D 2896. The concentration of the alkaline-earth metal phenates in the lubricating composition can vary depending upon the customer's requirements and applications. In a preferred embodiment of the invention, a practical alkaline-earth metal phenates use range in the lubricating composition is from about 500 parts per million to 50,000 parts per million (i.e. 0.05 to 5.0 wt %) based on the total weight of the lubricating oil composition, preferably the concentration is from 7,500 to 40,000 parts per million (ppm) and more preferably from about 9,000 to 27,000 ppm by weight.

[0061] Although the alkaline-earth metal phenates useful in the present invention fall into the general class of additives known as detergents, the phenates are not interchangeable with other detergents, i.e. sulfonates, as two detergents having the same TBN, molecular weight, metal ratio and the like, will have widely different performance characteristics in the present invention.

[0062] The metal sulfonate useful in the present invention is represented, e.g., by one of the general formulae

[0063] wherein, R₅ and R₆ are each a hydrocarbon group, which may be the same or different; and (n) is number of alkyl substituent(s) on the aromatic or naphthalene ring, and an integer of 1 to 5 or 1 to 7, respectively, preferably 1 to 2. The hydrocarbon group is an alkyl or alkenyl group having a carbon number of 8 to 28, preferably an alkyl group having a carbon number of 10 to 22. When the carbon number is below 8, the metallic detergent may not be sufficiently dissolved in the lubricant oil. When it exceeds 28, on the other hand, the acid-neutralizing function of the detergent may not increase as expected for its content, and may conversely cause problems, such as oxidation of the alkyl group in the metallic detergent, deteriorating the detergent itself into a deposit.

[0064] The metal sulfonate of the present invention is preferably a calcium sulfonate made from the salt of sulfonic acid having a hydrocarbon group (e.g., petroleum-derived sulfonic acid, and sulfonic acid having a long-chain alkyl benzene and alkyl naphthalene), and is not overbased.

[0065] The metal sulfonate for the lubricant oil composition of the present invention is preferably a calcium sulfonate provided at 0.5 to 5.0 wt % as the total content based on the whole composition, preferably at 0.5 to 3.0 wt % as the total content based on the whole composition, and more preferably at 0.5 to 1.0 wt. % as the total content based on the whole composition. At a total content below 0.5 wt. %, the detergent may have an insufficient lacquer control. When it exceeds 5.0 wt. %, on the other hand, its acid-neutralizing function may not increase as expected for its content, and may conversely cause problems, such as oxidation of the metallic detergent, deteriorating itself into a deposit.

[0066] Basic nitrogen-containing ashless dispersants useful in this invention include hydrocarbyl succinimides; hydrocarbyl succinamides; mixed ester/amides of hydrocarbyl-substituted succinic acids formed by reacting a hydrocarbyl-substituted succinic acylating agent stepwise or with a mixture of alcohols and amines, and/or with amino alcohols; Mannich condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines; and amine dispersants formed by reacting high molecular weight aliphatic or alicyclic halides with amines, such as polyalkylene polyamines. Mixtures of such dispersants can also be used. As used herein, the terms “aminated hydrocarbyl succinic derivatives” and “aminated polyalkenyl succinic derivatives” include all items listed in this paragraph.

[0067] Such basic nitrogen-containing ashless dispersants are well known lubricating oil additives, and methods for their preparation are extensively described in the patent literature. For example, hydrocarbyl-substituted succinimides and succinamides and methods for their preparation are described, for example, in U.S. Pat. Nos. 3,018,247; 3,018,250; 3,018,291; 3,172,892; 3,185,704; 3,219,666; 3,272,746; 3,361,673; and 4,234,435. Mixed ester-amides of hydrocarbyl-substituted succinic acid are described, for example, in U.S. Pat. Nos. 3,576,743; 4,234,435 and 4,873,009. Mannich dispersants, which are condensation products of hydrocarbyl-substituted phenols, formaldehyde and polyamines are described, for example, in U.S. Pat. Nos. 3,368,972; 3,413,347; 3,539,633; 3,697,574; 3,725,277; 3,725,480; 3,726,882; 3,798,247; 3,803,039; 3,985,802; 4,231,759 and 4,142,980. Amine dispersants and methods for their production from high molecular weight aliphatic or alicyclic halides and amines are described, for example, in U.S. Pat. Nos. 3,275,554; 3,438,757; 3,454,555; and 3,565,804.

[0068] In general amines containing basic nitrogen or basic nitrogen and additionally one or more hydroxyl groups, including amines of the types described in U.S. Pat. No. 4,235,435 can be used in the formation of the ashless dispersants. Usually, the amines are polyamines such as polyalkylene polyamines, hydroxy-substituted polyamines and polyoxyalkylene polyamines. Examples of polyalkylene polyamines include diethylene triamine, thiethylene tetramine, tetraethylene pentamine, pentaethylene hexamine, and dipropylene tiamine. While pure polyethylene polyamines can be used, it is generally preferred to use mixtures of linear, branched and cyclic polyethylene polyamines having an average in the range of about 2.5 to about 7.5 nitrogen atoms per molecule and more preferably an average in the range of about 3 to about 5 nitrogen atoms per molecule. Mixtures of this type are available as articles of commerce. Hydroxy-substituted amines include N-hydroxyalkyl-alkylene polyamines such as N-(2-hydroxyethyl)ethylene diamine, N-(2-hydroxyethyl)piperazine, and N-hydroxyalkylated alkylene diamines of the type described in U.S. Pat. No. 4,873,009. Polyoxyalkylene polyamines typically include polyoxyethylene and polyoxypropylene diamines and triamines having average molecular weights in the range of 200 to 2500.

[0069] Borated polyalkenyl succinimides are described in U.S. Pat. No. 4,863,624, which is herein incorporated by reference. Preferred borated dispersants are boron derivatives derived from polyisobutylene substituted with succinic anhydride groups and reacted with polyethylene amines, polyoxyethylene amines, and polyol amines (PIBSA/PAM) and are preferably added in an amount from about 1.0 to 10.0 wt %, more preferably about 1.5-6.0 wt %, and even more preferably in the amount of 1.75-3.0 wt % based on oil composition. These reaction products are amides, imides or mixtures thereof. Borated dispersants may provide benefits over non borated equivalents with respect to corrosion, rust, seal swell and wear.

[0070] Other additives such as other antioxidants, pour point depressants, viscosity index improvers, metal passivators, defoamants, friction modifiers, thickeners, emulsifiers, demulsifiers, dyes, corrosion inhibitors, acid sequestration agents, extreme pressure agents may be added without affecting the lacquer reducing performance of the current invention.

[0071] Lacquer formation is generally not a problem in natural gas engines running clean, dry methane of high Wobbe Index numbers. However, even in that case, the present formulation would still be useful as it would reduce lacquer formation caused by the unusual circumstances of excessively high or low engine temperatures combined with a non-optimized ali/fuel ratio. In a preferred example, the present invention is employed in natural gas engines that use less pure forms of natural gas, such as bio, wellhead, sewer, landfill and digester gas and other gas engines where lacquer formation is more often found. In general, the present invention is more useful when employing natural gas with a Wobbe Index of less than 30 MJoules/m³

EXAMPLES

[0072] A Caterpillar G3616 gas powered engine was operated on landfill gas employing a commercially available lubricant that contained both Group I and Group II base oils and a conventional additive set. After 16,249 hours of operation, two of the power cylinders were overhauled. During this time, the lubricant consumption had risen from the typical seven gallons per day to approximately 10 gallons per day. The cylinder liners were removed and split. Sections from the ring travel area (expected area of heavy lacquer formation) and areas at the bottom of the liners (essentially no lacquer formation) were removed and measured for surface roughness.

[0073] As expected, surface roughness was lower within the ring travel area due to the lacquer formation. Since the cylinder liner honing procedure and the resulting surface roughness may vary from one liner to the next, the surface roughness measurement at the bottom of each liner was used as a reference for that liner. The surface roughness for the ring travel areas was measured and the difference between the two measurements was calculated to show the change of surface roughness due to lacquering. With the commercially available lubricant, the average surface roughness delta was 0.73 micrometers.

[0074] The engine was placed back into operation, but now employing the formulation of the current invention. Over the 7,778 hours of operation the lubricant oil consumption remained at the typical 7 gallons/day. The cylinders were then removed and the comparable surface roughness measurements were taken. The formulation of the present invention produced a surface roughness delta of 0.15 micrometers.

[0075] Caterpillar's standard to evaluate the performance of a new lubricating oil formulation is to perform a 7,000 hour field test; the OEM has concluded that engine deposit levels, including cylinder liner lacquer, have achieved equilibrium after that many hours of operation. Using this standard, the cylinder lacquer formation employing the current invention was approximately one-fifth that of the commercially available lubricant. Even assuming that lacquer formation is linear over time (as opposed to the current theory that it reaches an equilibrium point), the formulation of the current invention produced approximately half the lacquer of the commercially available product. 

What is claimed is:
 1. A lubricating oil composition comprising: (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks; (b) a diarylamine; (c) an alkaline earth metal phenate; (d) an alkali earth metal sulfonate; (e) a borated aminated hydrocarbyl succinic derivative.
 2. The lubricant oil of claim 1 wherein the diarylamine is an alkylated diphenyl amine provided to said composition in a concentration of about 0.05 to2.0 wt %.
 3. The lubricant oil of claim 1 wherein the diarylamine is an alkylated diphenyl amine provided to said composition in a concentration of about 0.2 to 0.75 wt %.
 4. The lubricant oil of claim 1 wherein the alkaline earth metal phenate is a calcium based phenate provided to said composition in a concentration of about 0.05 to 5.0 wt %.
 5. The lubricant oil of claim 1 wherein the alkaline earth metal phenate is a calcium based phenate provided to said composition in a concentration of about 0.9 to 2.7 wt %.
 6. The lubricant oil of claim 1 wherein the alkali earth metal sulfonate is a calcium sulfonate provided to said composition in a concentration of about 0.5 to 5.0 wt %.
 7. The lubricant oil of claim 6 wherein the calcium sulfonate is a neutral calcium sulfonate provided to said composition in a concentration of about 0.5 to 1.0 wt %.
 8. The lubricant oil of claim 1 wherein said borated aminated hydrocarbyl succinic derivative is derived from succinic anhydride and provided to said composition in a concentration of about 1.0 to 10.0 wt %.
 9. The lubricant oil of claim 8 wherein the borated aminated polybutenyl succinic anhydride is provided to said composition in a concentration of about 1.75 to 3.0 wt %.
 10. The lubricant oil of claim 1 wherein said diarylamine is an alkylated diphenyl amine provided to said composition in a concentration of about 0.05 to 2.0 wt %, said alkaline earth metal phenate is a calcium based phenate provided to said composition in a concentration of about 0.05 to 5.0 wt %, said alkaline earth metal sulfonate is a calcium sulfonate provided to said composition in a concentration of about 0.5 to 5.0 wt %, said borated aminated hydrocarbyl succinic derivative is derived from succinic anhydride and provided to said composition in a concentration of about 1.0 to 10.0 wt %.
 11. The lubricant oil of claim 1 wherein said diarylamine is an alkylated diphenyl amine provided to said composition in a concentration of about 0.2 to 0.75 wt %, said alkaline earth metal phenate is a calcium based phenate provided to said composition in a concentration of about 0.9 to 2.7 wt %, said alkaline earth metal sulfonate is a calcium sulfonate provided to said composition in a concentration of about 0.5 to 1.0 wt %, said borated aminated hydrocarbyl succinic derivative is derived from succinic anhydride and provided to said composition in a concentration of about 1.75 to 3.0 wt %.
 12. A method of reducing lacquer in natural gas engines comprising employing the lubricant of claim
 1. 13. A method of reducing lacquer in natural gas engines comprising employing the lubricant of claim
 10. 14. A method of reducing lacquer in natural gas engines comprising employing the lubricant of claim
 11. 15. A lubricant oil composition comprising: (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks; (b) about 0.20 to about 0.75 wt % of an alkylated diphenyl amines; (c) about 0.9 to about 2.7 wt % of at least one overbased alkali-metal phenate sulfide; (d) about 0.50 to about 1.0 wt % of neutral alkali-metal sulfonate; and (e) about 1.75 to about 3.0 wt % of a borated aminated hydrocarbyl succinic derivative which is derived from a succinic anhydride
 16. A method of reducing lacquer in natural gas engines comprising employing a lubricant oil composition comprising: (a) at least about 20 wt % of at least one base oil of lubricating viscosity selected from the group consisting of Group II, Group III and Group IV base stocks; (b) about 0.20 to about 0.75 wt % of an alkylated diphenyl amines; (c) about 0.9 to about 2.7 wt % of at least one overbased alkali-metal phenate sulfide; (d) about 0.5 to about 1.0 wt % of neutral alkali-metal sulfonate; and (e) about 1.75 to about 3.0 wt % of a borated aminated hydrocarbyl succinic derivative which is derived from a succinic anhydride
 17. An additive for use in a lubricating oil composition which contains at least about 20 wt % of a non Group I base oil, said additive comprising: (a) a diarylamine; (b) an alkaline earth metal phenate; (c) an alkaline earth metal sulfonate; and (d) a borated aminated hydrocarbyl succinic derivative 